Conventionally, a technique of communicating various types of information through car-to-car communication has been proposed and practical use thereof is under consideration. Thus, various methods, devices, and the like, for detecting a distance through car-to-car communication are disclosed (see Patent Literature 1, for example).
In a communication device disclosed in Patent Literature 1: a common spreading code, which is common to a plurality of vehicles and used for transmissing information, is generated; a spreading code for distance measurement, which is different from the common spreading code, unique to each vehicle, and used for distance measurement, is generated; a code obtained by applying spread spectrum processing to information by using the common spreading code and the spreading code for distance measurement are summed; a result of the summing is converted into a radio band signal and transmitted into the air; a radio band signal reflected from the other vehicle or other objects is received and converted into a spread band signal; despreading is performed by using the spreading code for distance measurement; and distance measurement is performed based on a code obtained by the despreading.
In this communication device: a spreading code, which is unique to each vehicle and used exclusively for distance measurement, is provided separately from the common spreading code which is used for transmission of information; and this spreading code, which is constantly (periodically) generated, is transmitted while being added to an information signal which has been spread by the common spreading code. This enables distance measurement to be constantly and continuously performed while information is transmitted based on the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).